Experiments with general circulation models with no mountains, half mountains and full (modern) mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift. The experiments were motivated by geologic evidence for large, kilometer-scale uplift in the late Cenozoic in southern Asia and the American west, particularly within the last 10 m.y. In January the amplitude of the mid-latitude, upper tropospheric planetary waves increased with uplift, and the low-level winds were progressively blocked or diverted around the topographic features. In July the progressive uplift caused monsoonlike circulations to develop in the vicinity of the Colorado and Tibetan plateaus. Atmospheric heating rates, midtroposphere vertical motion, and upper-tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift. These result suggest that geologically recent kilometer-scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift. Comparison of the simulated climatic effects of uplift with the geologic evidence for late Cenozoic climatic change, especially for the last 10 m.y., is given in accompanying papers. ¿ American Geophysical Union 1989